Industrial preparation of hyroxylamine is usually carried out under a recycling system by combining with other processes, for example, the hydroxylamine-oxime reaction system. In this system, nitric acid and hydrogen are used as starting material, and phosphate salt is used as an inorganic processing solution. Nitrate ions are reduced to hydroxylamine in the presence of catalysts. The hydroxylamine obtained is subjected to a condensation reaction with cyclohexanone to give cyclohexanone oxime. After oxime is produced, nitric acid is added to the phosphate processing solution or nitrous gases is introduced and absorbed to form nitric acid, so as to increase the required amount of nitrate ions. Thereafter, the phosphate inorganic processing solution is introduced to a hydroxylamine reactor to generate hydroxylamine. These reactions are shown as follows:
Preparation of Hydroxylammonium Phosphate by the Reduction of Nitrate IonsNH4NO3+2H3PO4+3H2→NH3OH.H2PO4+NH4H2PO4+2H2OPreparation of Cyclohexanone Oxime by Condensation with CyclohexanoneNH3OH.H2PO4+C6H10O→C6H10NOH+H2O+H3PO4Supplement of Nitrate Ions into the Phosphate Inorganic Processing SolutionHNO3+H2PO4−→NO3−+H3PO4
Since the inorganic processing solution containing phosphate salt is recycled during the processing, the quality of the obtained hydroxylamine is directly affected by the quality of the inorganic processing solution. In the inorganic processing solution, phosphoric acid and phosphate salts are used as an acidic buffer solution. The metal impurities formed through the corrosion of apparatuses or other causes will be dissolved in the acidic buffer solution during the recycling processing and will decrease the selectivity of hydroxylamine production.
To illustrate, U.S. Pat. No. 3,767,758 describes that an inorganic processing solution containing molybdenum, rhodium or ruthenium causes a decrease of the selectivity of hydroxylamine production. Further, U.S. Pat. No. 4,062,927 discloses that when hydroxylamine is prepared by reduction of nitrate ions or nitrogen monoxide with hydrogen in an acidic solution, the acidic solution can corrode apparatuses or facilities, and thus causes the contamination with heavy metal. Among the heavy metal contaminants, molybdenum contaminants can cause 5˜15% decrease of the selectivity of hydroxylamine production. Therefore, the molybdenum contaminants are removed from the acidic solution by coprecipitation of the molybdenum contaminants together with the ion-ammonium phosphate precipitate.
However, the coprecipitation requires a pH of over 3.5 to give precipitates, and a basic solution is required to adjust the pH of the acidic inorganic processing solution used in the hydroxylamine-oxime recycling system. However, this treatment will increase the cost and the complexity of processes, and the selectivity of the hydroxylamine production is only promoted up to 83%.
Therefore, it is desired to provide a simple process with high selectivity for the preparation hydroxylamine.